Aging-associated insulin resistance predisposes to hypertension and its reversal by exercise: the role of vascular vasorelaxation to insulin.
Aging is an independent risk factor for hypertension, and hypertension and insulin resistance commonly coexist in the elderly. This study was designed to examine the effects of aging-related insulin resistance on blood pressure (BP) and its underlying mechanisms, with specific focus on the role of exercise in reversing hypertensive response. Adult (6-month-old) and aging (24-month-old) male Sprague-Dawley rats were subjected to a 10 weeks free-of-loading swim training (60 min/day, 5 days/week). Arterial vasorelaxation, cardiac contraction, eNOS activation, and iNOS and gp91(phox) expression were determined. Under aging-related insulin resistance conditions, insulin infusion significantly elevated BP (P < 0.05). Aging caused significant endothelial dysfunction (P < 0.05 - 0.01), which was responsible for decreased arterial vasorelaxation to insulin. Aging attenuated myocardial contractile response to insulin, decreased eNOS expression and its phosphorylation by insulin, and increased iNOS and gp91(phox) expression in aging arteries (P < 0.01). Exercise improved insulin sensitivity, potentiated insulin's positive inotropic effects, facilitated arterial vasorelaxation to insulin, increased arterial eNOS activation in adult and aging rats, and thus attenuated insulin resistance-related hypertensive response to insulin. Moreover, exercise markedly reversed increased iNOS and gp91(phox) expression in aging arteries. Inhibition of eNOS with Cavtratin or L-NAME significantly blocked exercise-facilitated arterial vasorelaxation to insulin and exercise-lowered BP response to insulin. In conclusion, these results demonstrate that endothelial dysfunction in response to insulin, but not insulin's positive inotropic effects, plays an important role in the development of aging-related hypertension. The reversal of hypertensive response to insulin by exercise is most likely associated with improved insulin sensitivity in an eNOS-dependent manner and reduced oxidative and nitrative stresses.
Li
Qiu-Xia
QX
Institution of Physical Education, Shaanxi Normal University, Xi'an, China.
Xiong
Zheng-Ying
ZY
Hu
Bai-Ping
BP
Tian
Zhen-Jun
ZJ
Zhang
Hai-Feng
HF
Gou
Wen-Yi
WY
Wang
Hai-Chang
HC
Gao
Feng
F
Zhang
Quan-Jiang
QJ
D000375:Aging / Q000502:physiology*; D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000378:metabolism; D001794:Blood Pressure; D015153:Blotting, Western; D006973:Hypertension / Q000209:etiology* / Q000503:physiopathology; D007150:Immunohistochemistry; D007328:Insulin / Q000494:pharmacology; D007333:Insulin Resistance / Q000502:physiology*; D008297:Male; D009206:Myocardium / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
D007328:Insulin; D052247:Nitric Oxide Synthase Type II; D052250:Nitric Oxide Synthase Type III